Many to Many && One to One

One-to-one would be handled by not inserting multiples into the child table. It's not currently enforced in any way, though I can envision having the ReferenceField being a single item instead of an entity might be used to implicity notify the framework
that's what you want.

There is no inherent many-to-many capability right now. It's something I've been thinking about, but since the project I developed this framework in conjunction with didn't actually have any many-to-many reationships, I've not committed any serious
time to resolving it. If you have suggestions or ideas on what you would like to see, I'd love to hear them.

I am currently evaluating using this tool on a project in which I have several many-to-many relationships. I noticed that you added a ReferenceType property to the FieldAttribute; however, the documentation ignores this and doesn't provide any examples.
Is this now supported, or is this merely a placeholder?

Unfortunately, the ManyToMany ReferenceType is currently only a placeholder. That said, another user is implementing many-to-many, so it's always possible we'll get a patch submission or at least some direction in how he attacked it.